A human machine interface (HMI) provides a means for interaction between the functioning parts of a device and a human operator. Historical examples include buttons and dials used to engage or disengage functions or to adjust parameters of the device function. Modern examples of the HMI have become more sophisticated, including electronic displays, interactive touch screens, and immersive environments such as augmented reality systems. However, advanced HMIs impose constraints, including design cost and complexity, and require investment in user training, which prevent their use in many applications. Industrial control equipment, such as motor overload relays, motor controllers, motor starters, circuit breakers, timers, and contactors, are example applications where HMI design features typically emphasize low functionality and low complexity.
Modern industrial control includes remote control over communication networks, to make remote adjustments to industrial control equipment. A remote HMI communicating over a network connection, enables changing configurations or control capabilities of industrial control equipment, such motor overload relays. By contrast, a local HMI situated near the industrial control equipment, enables local visual confirmation of operations and responses to control inputs, which may facilitate maintenance and inspection operations not otherwise easily accomplished remotely. A local HMI may allow an equipment installer to select values for settings prior to the complete commissioning of the equipment and network, without needing to apply control power to remotely control the devices being configured.
A problem with prior art industrial control systems that provide both local and remote HMI, is the inability to establish consistent settings between local and remote parameter adjustments, without adding significant complexity to the control system. In the example of a motor full load current (MFLC) setting for an overload relay, an example state of the art local HMI is a manually turned dial. The MFLC parameter is easily set to a desired value at a local HMI by rotating the dial to an indicated position. However, with the addition of a remote HMI, the traditional dial becomes inadequate as a local HMI. For example, the local HMI may indicate a parameter value that is invalid, based on the remote HMI setting, if the device parameter is changed remotely and the local HMI setting is not correspondingly updated.
Various prior art approaches exist to address the complication of control systems with local and remote HMIs. One prior art approach is to motorize the local HMI to adjust for parameter adjustment made by the remote HMI. However, this adds significant cost and complexity to the design. Another prior art approach is to accept the discrepancy of the parameter value between local and remote HMI displays, and to assign a prioritization for the value selected by either the local or remote HMI. However, this does not remove the discrepancy and presents inaccurate information about the parameter setting on the local HMI. Another prior art approach is to replace the dial with an interactive electronic display, which may maintain consistency with the remote HMI. However, this adds cost and complexity to the design, and requires special consideration during the powered-down state of the equipment at the time of its installation, since some power is needed to operate the local HMI.